You have your choice really,
Tires that work really good and don't last too long, or tires that work okay and last longer.
I used to run the MT-18 Pirrelli's with the 4mm Bridgestone tubes and slime, but, since they switched to the XCMH designation they are crap as far as how well they work. They are a heavy tire, and if you are looking for tire that is very flat resistant then they are a good choice. And since they are heavy they increase the un-sprung weight, so it affects how your suspension works.
I have since switched to the Bridgestone 403/404 tires with the 4mm Bridgestone tubes and slime. I run them at 13 psi max, and they work great! Night and day difference between the Pirrelli's. They are a much lighter tire and as such their effect on suspension action is also noticeable, E.G. the wheels follow the ground much better. And since they are a more compliant tire, the overall ride is noticeably more plush. The first time I tried them out was after the 6 hours of Glen Helen, and I thought my suspension oil was shot and needed service.
These tires have excellent traction and hold up well in the rocks with minimal rear tire chunking, and front tire side knob tearing. The last race I rode on them was a pretty grueling National Hare and Hound here in So Cal that was mostly just rocks on the second and third loops. While the tires showed wear, they still were working good.
My next move will be to install bib mousses in them and try them out, along with a set of Michelin XC-12's before this years Idaho City 100. That way I don't have to carry a flat fixing kit, and more importantly don't have to worry about flats.